When a register for events node runs, it creates a queue of all the events it registered and returns a reference which you can use (you can wire it into the dynamic event terminal on a case structure).
The details of the queue are all handled behind the scenes, but I'm guessing it's probably a 32 bit length (which, on a machine with 32 bits of address space, means you'd run out of memory long before you fill the queue). In any case, it should be "large enough" for anything you would want to use it for.
There are documents online and in the LabVIEW help on the use of user events, so you should search for and read those. There are probably also examples in the example finder (Help>>Find Examples).
One important thing to remember is NEVER to wire the reference from a register node into more than one event structure. You can do it techincally, but you'll lose events without realizing it.
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